APPARATUS AND METHOD FOR CONTROLLING A SINTERING PROCESS

Abstract

An apparatus (150) for controlling a sintering process in a sintering furnace (100), includes a preheating zone (120) and a high heat zone (130), further comprising at least two measuring devices (151, 152, 153, 154), wherein the at least two measuring devices comprise at least one measuring device in the preheating zone (120) and at least one measuring device in the high heat zone (130) for analyzing a furnace atmosphere at the respective zone, and adjusting means (155, 156) for adjusting a composition of the furnace atmosphere based on measurement values acquired by the at least two measuring devices (151, 152, 153, 154) in the respective zones (110, 120, 130, 140).

Claims

1-12. (canceled)

13. An apparatus (150) for controlling a sintering process in a sintering furnace (100), comprising: a pre-heating zone (120) and a high heat zone (130); at least two measuring devices (151, 152, 153, 154), the at least two measuring devices comprising at least one measuring device in the pre-heating zone (120) and at least one measuring device in the high heat zone (130) for analyzing a furnace atmosphere at a respective one of the zones; and adjusting means (155, 156) for adjusting a composition of the furnace atmosphere based on measurement values acquired by the at least two measuring devices (151, 152, 153, 154) in the respective zones (110, 120, 130, 140).

14. The apparatus (150) according to claim 13, wherein the at least two measuring devices (151, 152, 153, 154) comprise devices selected from the group consisting of oxygen analyzers (151), dew point analyzers (152), lambda probes (153), and hydrogen analyzers (154).

15. The apparatus according to claim 13, wherein the at least two measuring devices (151, 152, 153, 154) are devices selected from the group consisting of an oxygen analyzer (151) in the high heat zone (130), and a dew point analyzer (152) in the pre-heating zone (120).

16. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere by altering humidity in the furnace atmosphere.

17. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere by altering at least one of concentrations of hydrogen, nitrogen and propane in the furnace atmosphere.

18. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere by altering humidity and at least one of concentrations of hydrogen, nitrogen and propane in the furnace atmosphere.

19. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere based on a carbon potential and an oxygen concentration in the furnace atmosphere.

20. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere based on a carbon potential, and a hydrogen ratio curve in the furnace atmosphere.

21. The apparatus (150) according to claim 13, wherein the adjusting means (155, 156) are adapted to adjust the composition of the furnace atmosphere based on a carbon potential, an oxygen concentration and a hydrogen ratio curve in the furnace atmosphere.

22. A sintering furnace (100), comprising an apparatus (150) for controlling a sintering process in a sintering furnace (100), the apparatus comprising: a pre-heating zone (120) and a high heat zone (130); at least two measuring devices (151, 152, 153, 154), the at least two measuring devices comprising at least one measuring device in the pre-heating zone (120) and at least one measuring device in the high heat zone (130) for analyzing a furnace atmosphere at a respective one of the zones; and adjusting means (155, 156) for adjusting a composition of the furnace atmosphere based on measurement values acquired by the at least two measuring devices (151, 152, 153, 154) in the respective zones (110, 120, 130, 140).

23. The sintering furnace (100) according to claim 22, wherein the sintering furnace (100) is a furnace selected from the group consisting of a sintering furnace for sintering metal injection molding parts, and a sintering furnace for powder metal sintering.

24. A method for controlling a sintering process in a sintering furnace (100), comprising: analyzing a pre-heating zone (120) and a high heat zone (130) of a furnace atmosphere by at least two measuring devices (151, 152, 153, 154), the at least two measuring devices comprising at least one measuring device in the pre-heating zone (120) and at least one measuring device in the high heat zone (130); and adjusting a composition of the furnace atmosphere based on measurement values acquired by the at least two measuring devices (151, 152, 153, 154) in the respective zones (110, 120, 130, 140).

25. The method according to claim 24, wherein the analyzing the furnace atmosphere comprises at least one of measuring an oxygen concentration, measuring a hydrogen concentration, measuring a dew point temperature, and measuring a lambda ratio.

26. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere comprises altering a humidity in the furnace atmosphere.

27. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere comprises altering at least one of concentrations of hydrogen, nitrogen and propane in the furnace atmosphere.

28. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere comprises altering a humidity and at least one of concentrations of hydrogen, nitrogen and propane in the furnace atmosphere.

29. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere is based on a carbon potential and an oxygen concentration in the furnace atmosphere.

30. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere is based on a carbon potential and a hydrogen ratio curve in the furnace atmosphere.

31. The method according to claim 24, wherein the adjusting the composition of the furnace atmosphere is based on a carbon potential, an oxygen concentration, and a hydrogen ratio curve in the furnace atmosphere.

32. The method according to claim 24, further comprising using the method for a process selected from the group consisting of sintering metal injection molding parts, and sintering powder metals.

Description

DESCRIPTION OF THE DRAWING

[0026] FIG. 1 shows a sintering apparatus with an apparatus for controlling a sintering process according to the invention in a preferred embodiment.

EMBODIMENT OF THE INVENTION

[0027] In FIG. 1, a schematical drawing of a sintering furnace 100, for example for sintering metal injection molding parts, is shown. Parts 180, 181 are placed on a bench 101 after metal injection molding and transported, e.g. by a conveyor, from the left end of the bench 101 to the right end of the bench 101.

[0028] Parts 180, 181, which are exemplarily shown in the sintering furnace 100, thus pass through different zones of the sintering furnace 100. These zones comprise an entry zone 110 at the beginning, followed by a pre-heating zone 120, a subsequent high heat zone 130 and a cooling zone 140 at the end.

[0029] An apparatus 150 for controlling the sintering process in the sintering furnace 100 is placed, for example, near the bench of the sintering furnace 100. The apparatus 150 comprises, for example, six measuring devices. These measuring devices are an oxygen analyzer 151 in the high heat zone 130, a dew point analyzer 152 in the pre-heating zone 120, a lambda probe 153 in the cooling zone 140, a hydrogen analyzer 154 in the cooling zone 140, a lambda probe 153 in the entry zone 110 and a hydrogen analyzer 154 in the entry zone 110.

[0030] The apparatus 150 is adapted to receive values measured by these six measuring devices and is further adapted to control adjusting means 155, 156. The adjusting means 155, 156 are placed at inlets 105, 106, which inlets are used for supply a gas mixture to the zones of the sintering furnace 100. This gas mixture is used as a furnace atmosphere for the sintering process or to alter an existing furnace atmosphere.

[0031] By controlling the adjusting means, the composition of the gas mixture in the sintering furnace, i.e. the furnace atmosphere, may be altered based on values measured by the measuring means 151, 152, 153 and 154.

[0032] In particular, the amount and relative composition of a hydrogen, humidty, nitrogen and propane mixture may be adjusted based on a formula of carbon potential versus values measured by the oxygen analyzer and a hydrogen ratio curve which determines the activation of the metal injection molding (MIM) lubricants to desolve in a debinding stage in the pre-heating zone 120 (also called debinding zone) of the furnace. The debinding of the plastic binding material is reacting with hydrogen and the water vapour (H2O), therefore the amount of humidity is calculated based on a basic stoichiometric calculation of the amount of water needed to burn of the plastic at an elevated temperature up to 800 C. The composition of the humidy or free oxygen is calculated by the weight of powder mix (so-called brown component) going in as a furnace charge. Then the amount of plastic present and then the amount of humidity to burn this off from the brown part is calculated. The flow rates of the debinding zone are then changed by changing the nitrogen or hydrogen carrier gas passing through a gas humidifier hence providing the necessary water content.

[0033] In the meantime the humidity content in the pre-heating (debinding) zone is continuously measured to keep the values constant hence making sure the environment has enough humidty to burn off (react with) the plastic input to the furnace. This will remove all plastic binders allowing the base powder mix to enter the high heat (sintering) zone with the right carbon content. The apparatus then will maintain the base level carbon content by creating a carbon neutral atmosphere.